Acetylcholine is one of the main neurotransmitters. It is involved in autonomic activities of the peripheral organs and forms a part of complicated neural networks in the central nervous system. Anticholinergic drugs are used in the treatment of various diseases, and many drugs have anticholinergic side effects. Thus, estimating the total burden of anticholinergic activity of drugs is important to assess the related adverse effects for patients taking such drugs. Serum anticholinergic activity (SAA) is measured using a competitive radioreceptor binding assay of muscarinic receptors. In addition to this direct measurement, several drug scales like the Anticholinergic Drug Scale (ADS), Anticholinergic Cognitive Burden Scale (ACB), and Anticholinergic Risk Scale (ARS) have been developed to estimate the total anticholinergic burden of drugs. These measurements have been used to demonstrate that certain drugs may be responsible for the cognitive impairment in the elderly or certain groups of patients with neurologic disorders. Clinicians should be aware of the impact of such drugs because central adverse effects are often obscure in these patient groups and are easily overlooked.